Direct Laser Interference Patterning (DLIP) and Laser Induced Period Surface Structures (LIPSS) are two distinct technologies for periodic surface texturing. Based on different physics phenomena, they enable structures often showing dissimilar morphology and pitch. It has been reported the possibility of superposing LIPSS over DLIP with a final multiscale, hierarchical morphology where the two structures coexist. Here, we report a novel approach in DLIP structuring based on the use of a galvo scanner with large aperture (30 mm) and an F-theta lens combining large entrance pupil (< 20 mm) and relatively small focal length (30 mm). We show that by using a 10 ps laser source emitting at λ=1064 nm, this set-up makes possible a DLIP pitch value Λ as low as 1.4 μm which become comparable with the LIPSS period ≈ 800 – 900 nm. Interestingly, in these experimental conditions, we identified a process window (fluence, number of passes, polarization) where LIPSS formation on stainless-steel surface is strongly affected by the presence of DLIP. Two highly homogeneous, uninterrupted, regular LIPSS arise between two successive DLIP crests with a period reduced to 470 nm, which is sensibly lower than expected. As a result, highly regular ripples with a narrow angular distribution and having a period < λ/2 are observed. Finally, all the generated structures have been characterised by SEM and FFT. We believe that our results represent a promising approach for the high throughput generation over large surface of highly regular structures in the range of few hundreds of nm.
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